Microwave oven field alteration



June 23, 1970 J. R. GIACOBBE ,51 5

MICROWAVE OVEN FIELD ALTERATION Filed Oct. 14, 1968 W 21MB 10W 1 aw,

ATTOR N EYS United States Patent 3,517,152 MICROWAVE OVEN FIELD ALTERATION Joseph R. Giacobbe, Dedham, Mass., assignor to Sage Laboratories, Inc., Natick, Mass., a corporation of Massachusetts Filed Oct. 14, 1968, Ser. No. 767,215 Int. Cl. H05b 9/06 US. Cl. 21910.55 2 Claims ABSTRACT OF THE DISCLOSURE A square or rectangular conductive sheet is spaced roughly one quarter wavelength from one wall of the microwave oven cavity and rotated roughly about its center.

BACKGROUND OF THE INVENTION The present invention relates in general to microwave oven field alteration and more particularly concerns a novel stirrer that is effective electrically and simple structurally. An embodiment of the invention exhibits greatly improved performance, especially when thawing and cooking raw meat, for reasons not fully understood.

It is an important object of this invention to provide microwave oven field alteration means that is highly effective from the standpoint of performance.

It is a further object of the invention to provide field alteration means in accordance with the preceding object that is simple structurally.

SUMMARY OF THE INVENTION According to the invention, a rectangular conductive sheet is spaced roughly one or an odd number of quarter wavelength from one wall of the microwave oven cavity. Means are provided for rotating the conductive sheet roughly about its center.

Numerous other features, objects and advantages of the invention will become apparent from the following specification when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The single figure of which is a perspective view of an exemplary embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS With reference now to the drawing, there is shown a microwave oven 11 having a rectangular stirrer 12 suspended from a shaft 13 rotatably supported in the upper wall 14 of the microwave oven cavity so that the distance between rectangular conducting plate 12 and upper wall 14 is substantially a quarter wavelength at the frequency of the microwave energy introduced into the oven to perform the heating. The specific details of the means for rotatably supporting and rotating shaft 13 are well known in the art and not shown in the figure so as not to obscure the principles of the invention.

3,517,152 Patented June 23, 1970 It has been discovered that the present invention provides greatly improved performance for uniformly heating food inside the oven, especially for thawing and cooking raw meat. It is not fully understood why these remarkable results are obtained with the invention. It is believed that a combination of effects may produce these results. As sheet 12 rotates, there is a shift of effective resonant frequencies of the internal cavity caused by effectively changing the cavity dimensions. The rectangular conducting plate 12 effectively forms a strip line transmission line that is continually reoriented to continually direct power to different portions of the cavity. In a specific embodiment of the invention dimensions used successfully in a 12" X 12" x 7 /2" cavity have included sheets 6%" X 6%" and 4 /2" x 4%", and A thick corresponding to a perimeter of said conducting sheet being in the order of one third to one half the perimeter about said cavity defining walls with an operating frequency of 2450 mHz. :25 mHz. It was discovered that the larger sheet may have had a slightly more uinform cooking pattern; however, the smaller one gave a better R-F impedance match to the magnetron tube source.

There has been described an especially effective field alteration means for a microwave oven. It helps provide uniform heating within the oven and improved R-F impedance match. Yet it is relatively inexpensive and easy to fabricate, support and rotate. It is evident that those skilled in the art may now make numerous uses and modifications of and departures from the specific embodiments described herein without departing from the inventive concepts. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features present in or possessed by the apparatus and techniques herein disclosed and limited solely by the spirit and scope of the appended claims.

What is claimed is:

1. In a microwave oven having walls defining a cavity for heating food in an RF field,

field alteration means comprising a rectangular conducting sheet substantially an odd number of quarter wavelengths from one of the walls defining the cavity, and

means for rotating said conductive sheet substantially about its center.

2. Field alteration apparatus in accordance with claim 1 wherein said one wall is the top Wall of said cavity and the perimeter of said conducting sheet is of the order of one third to one half the perimeter about said cavity defining walls.

References Cited UNITED STATES PATENTS 1/1960 Haagensen 21910.55 1/1968 Reftmark 2l9-10u55 

